1. Field of the Invention
At least one embodiment of the invention generally relates to medical device safety method and more particularly, but not by way of limitation, relates to a method for determining if an implantable medical device is magnetic resonance conditional and hence poses no hazards with respect to a specified magnetic resonance imaging environment with specified conditions of use.
2. Description of the Related Art
Traditional methods for determining if an implanted medical system is “Magnetic Resonance (MR) conditional” are time consuming, costly and in many cases involve unbillable tasks. For example, recognized solutions require multiple physicians to potentially determine information that should be known at implant time. Furthermore, recognized solutions do not ensure that conservative settings are enforced in cases where programming is not completed at implant time. In addition, typical solutions fail to periodically update external databases with status, e.g., nightly during home monitoring uploads, and thus may not reflect the current status of the implanted system.
An MR conditional system, for example, is a system that has been demonstrated to pose no known hazards in a specified Magnetic Resonance Imaging (MRI) environment with specified conditions of use. Example conditions that define the MRI environment include static magnetic field or specific absorption rate (SAR) for example. In order for a system to be MR conditionally safe, both the implanted medical device and associated leads need to be MR conditional, without any non-MR conditional abandoned leads or other non-MR conditional hardware implanted in the patient. Furthermore, the MR conditions for which a system is approved for vary, and are a function of both the specific implantable device and implanted leads.
An “MR Safe” system, for example, is a system that poses no known hazards in all MR environments. Example MR Safe materials include non-conducting, non-metallic and non-magnetic materials such as plastic.
An “MR Unsafe” system, for example, is a system known to pose hazards in all MRI environments. Example MR unsafe materials include some conductive electrode leads and ferromagnetic materials. Due to the extreme strength of magnetic fields used for MRIs, ferromagnetic materials are generally considered dangerous in the MR environment and have been known to cause the so called “missile-effect”, where ferromagnetic materials are accelerated in the magnetic field to dangerous kinetic energies.
Before a radiologist performs an MRI on a patient having a cardiac rhythm management (CRM) device or other implantable medical device or system, the radiologist must determine if the implanted system is MR conditionally safe. Since there is no known easy manner for determining if the implanted system is MR conditionally safe, the radiologist either does not give the patient the MRI, or alternatively, calls the implanting cardiologist to ask whether the system is MR conditional.
If no MRI occurs, the patient may be denied a procedure that is beneficial, life extending or life saving, simply because the radiologist does not have information that should be known a priori regarding the implanted system.
Alternatively, the radiologist may call the cardiologist who looks through the patient files, and generally receives no reimbursement for this task. However, a phone call to the implanting physician or cardiologist has disadvantages. The implanting physician generally does not want to be bothered with phone calls every time a patient needs to be cleared for an MRI. Phone calls tend to take up the time of the implanting physician's staff, and are generally not billable.
In this scenario, the implanting cardiologist may read the patient's file and may write a memo to the radiologist indicating whether the system is MR conditional or not. If the records cannot be found, for example if the patient has changed cardiologists, then the cardiologist will order a chest X-ray to look for X-ray markers, devices and abandoned leads and, in combination with device interrogation, the cardiologist may attempt to determine if the implanted system is an MR conditional safe system. This occurs even though the data regarding the implanted system should be known a priori. However, X-rays have well known risks, added costs, and tend to complicate the MRI workflow. Furthermore, different X-ray markers are required to indicate if a system is conditionally safe for 1.5 T, 3.0 T, both 1.5 T & 3.0 T, up to 2 W/Kg, up to 4 W/Kg, with exclusion zone, without exclusion zone, etc. It is difficult to make so many distinctions in small X-ray markers, which limits their usefulness.
In summary, there is no consistent manner in which to identify if an implanted system is MR conditional, and what the conditions are. Therefore, some patients who have MR conditional systems are denied MRI scans because of the difficulty in verifying that their implanted systems are MR conditional, and many patients are denied MRIs today who would benefit from them. Hence, there is a need for a method for determining if an implantable medical device is magnetic resonance conditionally safe.